The present invention generally relates to a manufacturing apparatus and method for a multilayer disc such as an optical recording medium or the like.
The multilayer structure made of multiple discs is used in an optical recording medium for example, and more specifically, in the so-called DVD (digital versatile or video disc) and the like.
Such a multilayer disc is formed by bonding multiple discs together with their central holes being centered to each other.
More particularly, two discs are held by different holders, respectively, central holes in the discs are centered with each other, and then the discs are bonded with a glue to each other. The multilayer disc manufacturing apparatus has a common centering pin to center the discs at their central holes with each other. Namely, the centering pin is introduced into the central holes in the two discs to make the central holes concentric with each other for aligning the discs at the central holes thereof with each other.
When the centering pin is thus used to align the two discs at their central holes with each other, a fitting clearance will take place without fail between the inner wall of each of the central holes and the centering pin. Since the clearance varies from one radial direction of another of the centering pin in each of the discs, such a clearance error will result in an eccentricity of the rotation center of each misalignment between the rotation centers of the discs bonded to each other.
The eccentricity of the rotation center of each disc is called xe2x80x9crotational eccentricityxe2x80x9d. If the rotational eccentricity exceeds a given range, there will result a defective multilayer disc from which a signal detector cannot detect any recorded signal.
To avoid the above, two discs have to be bonded to each other for the rotational eccentricity to fall within a given range in which the signal detector can detect signals from the discs.
However, as the number of discs in a multilayer disc is increased, the above rotational eccentricity will be cumulated and cannot be maintained to fall within the given range. Also, in the case of a xe2x80x9cDVR (digital video recording)xe2x80x9d disc incorporating multiple discs one of which is formed from a sheet-shaped disc smaller in thickness than the other disc, the centering pin fitted in the central hole formed in the thin sheet-shaped disc will possibly damage the latter.
Further, the rotational eccentricity is conventionally computed based on a maximum run-out of the disc being actually rotated. Therefore, to rotate the disc for this purpose, the multilayer disc manufacturing apparatus has to include a disc rotating mechanism and rotation guide mechanism, which will add to the complexity of the apparatus, thus resulting in the size and costs of the apparatus.
Rotating the disc actually as above will increase the tact time and thus increase the manufacturing costs for the multilayer disc.
Accordingly, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing a multilayer disc manufacturing apparatus and method capable of computing the rotational eccentricity of a disc with no contact with the disc and a high accuracy and producing the disc with less costs without having to rotate the disc or any complicated operations.
The above object can be attained by providing an apparatus for manufacturing a multilayer disc by bonding one disc to another disc, the apparatus including according to the present invention:
means for fixing the one disc in place;
means for projecting a light onto a boundary between an embossed signal recording area and a non-signal recording area on the one disc fixed in place;
means for capturing a return light from the boundary illuminated with the light projected from the light projecting means;
means for positioning the center of a signal recording area on the other disc; and
means for varying the position of the centering means in relation to the disc fixing means.
In an embodiment of the present invention, light is projected onto the boundary between the embossed signal recording area and the non-signal recording area with the one disc being fixed by the disc fixing means. The light incident upon the boundary is reduced in intensity along the axis of the light due to a reflection at, or transmission through, the embossed signal recording area under a phenomenon of diffraction.
By capturing a return light reduced in intensity and a one not reduced in intensity by the return light capturing means, the center of the signal recording area on the one disc can be computed.
Based on the thus computed center of the signal recording area on the one disc, the relative position varying means is moved. Then, the center of the signal recording area on the one disc is made coincident with that of the signal recording area on the other disc to compute the rotational eccentricity of the one disc with no contact with the disc and a high accuracy and thus to accurately limit the rotational eccentricity of the multilayer disc to fall within a given range.
Also, the above object can be attained by providing a multilayer disc manufacturing apparatus wherein the disc fixing means is preferably a suction unit to fix the one disc by suction, the centering means is a centering pin, and the relative position varying means is a biaxial stage laid in a plane parallel with the one disc.
Also, in this construction, the disc fixing means is a suction unit to fix the one disc by suction. It can fix the one disc easily and positively. The centering means is a centering pin also capable of positioning the center of the other disc easily and positively. Further, the relative position varying means is a biaxial stage laid in a plane parallel with the one disc. By moving the stage biaxially, the one disc can be moved easily and positively.
Also, the above object can be attained by providing a multilayer disc manufacturing apparatus wherein the centering pin preferably has a taper portion whose diameter is smaller towards the free end thereof.
In the construction of another embodiment, the taper portion of the centering pin, whose diameter is smaller towards the free end thereof, permits positioning of the other disc for no fitting clearance to take place between the inner wall of the central hole, for example, and the centering pin. Thus, the rotational eccentricity of the other disc can be minimized.
Also, the above object can be attained by providing a multilayer disc manufacturing apparatus wherein multiple centering pins of different diameters are available.
In this construction the multiple centering pins of different diameters are compatible with multiple types of the other disc having central holes different in inside diameter from each other.
Also, the above object can be attained by providing a multilayer disc manufacturing apparatus wherein the light projecting means projects light generally vertically onto the surface of the one disc and the return light capturing means captures return light generally vertically reflected from the surface of the one disc.
In this construction, a difference in amount of light reflected under the phenomenon of diffraction in the signal recording area can accurately be captured even when a signal in the embossed signal recording area of the one disc is densely recorded with narrow track pitches and the one disc is a translucent low-reflection sheet, for example.
Also, the above object can be attained by providing a multilayer disc manufacturing apparatus wherein the one disc is a sheet-shaped disc while the other disc is a substrate-like disc, and the sheet-shaped disc is formed thinner than the substrate-like disc.
In this construction, the sheet-shaped disc, easily damageable, is centered not by the central hole formed therein and the centering pin, so that the sheet-shaped disc itself will not possibly be damaged at all as with the prior art.
Also, the above object can be attained by providing a method for manufacturing a multilayer disc by bonding one disc to another disc, the method including, according to the present invention, the steps of:
fixing the one disc in place by a fixing means;
projecting, by a light projecting means, a light onto a boundary between an embossed signal recording area and non-signal recording area on the one disc fixed in place;
capturing, by a return light capturing means, a return light from the boundary illuminated with the light projected from the light projecting means;
determining the center of the signal recording area on the one disc based on information as to the signal recording area, acquired in the return light capturing step;
moving means for varying the position of the means for positioning the center of the signal recording area on the other disc in relation to the disc fixing means in order to align the center of the signal recording area of the one disc, determined in the area center determining step, with the centering means; and
bonding the one disc and the other disc to each other.
In the above method, the light is projected onto the embossed signal recording area on the one disc with the one disc being fixed by the disc fixing means. The incident light is reduced in intensity along the axis of the light due to a reflection at, or transmission through, the embossed signal recording area under a phenomenon of diffraction.
In the return light capturing step in which a return light reduced in intensity and a one not reduced in intensity are captured and the area center determining step, the center of the signal recording area on the one disc can be-computed.
To align the center of the signal recording area on the one disc, which was determined in the area center determining step with the centering means for positioning the center of the signal recording area on the other disc, the center of the signal recording area on the one disc is made coincident with that of the signal recording area on the other disc in the relative position varying means moving step to correct the rotational eccentricity.
In the disc bonding step, the one disc and the other disc are bonded to each other.
Thus, the rotational eccentricity of the one disc can be computed with no contact with the disc and a high accuracy, and the rotational eccentricity of the multilayer disc can be limited accurately to fall within a given range.
Also, the above object can be attained by providing a multilayer disc manufacturing method wherein the return light capturing means include multiple CCD cameras and the rotational eccentricity is computed based on the information captured by the multiple cameras in the area center determining step.
In this method the rotational eccentricity can be computed with a higher accuracy. Therefore, the rotational eccentricity can be corrected with a higher accuracy.
Also, the above object can be attained by providing a multilayer disc manufacturing method wherein the light projecting means projects light generally vertically onto the surface of the one disc and the return light capturing means captures a return light generally vertically reflected from the surface of the one disc.
Also, the above object can be attained by providing a multilayer disc manufacturing method wherein the one disc is a sheet-shaped disc while the other disc is a substrate-like disc, and the sheet-shaped disc is formed thinner than the substrate-like disc.